The present invention is directed to ink compositions, and imaging and printing processes thereof. More specifically, in embodiments the present invention is directed to ink jet ink compositions with improved latency characteristics useful for printing on a variety of papers and substrates, and wherein the inks contain dendrimer grafts, such as dendrimers grafted with nonionic alkylene oxide oligomers. The inks can be formulated after mixing water, and the grafted dendrimer by the addition, for example, of a cosolvent comprised of water and a glycol, like ethylene glycol, diethylene glycol, thereby improving latency, which is the maximum time period as illustrated herein, over which an uncapped ink jet printhead can remain idle before noticeable deterioration of its jetting performances. Also, the addition of glycol permits the adjustment of the ink viscosity from about 1.1 to about 5 centipoise, and preferably from about 1.1 to about 3.0 centipoise, and can permit adjustment of the ink surface tension. Viscosity and surface tensions are important contributing factors in the production of excellent quality prints on plain papers, that is prints with acceptable edge acuity, or the sharpness of the edge between the printed and nonprinted areas, minimal ink feathering on paper, and characterized, for example, by a desirable uniformity of solid area ink coverage. The inks of the present invention can be selected for a number of known ink jet printing methods and apparatus, including thermal ink jet, or bubble jet processes as described in, for example, U.S. Pat. No. 4,601,777, U.S. Pat. No. 4,251,824, U.S. Pat. No. 4,410,899, U.S. Pat. No. 4,412,224, and U.S. Pat. No. 4,532,530, the disclosures of which are totally incorporated herein by reference. Rapid drying and excellent waterfastness, in embodiments of the present invention from between 90 to about 99 percent, are of value in rapid printing applications such as printing by xerography at a speed of 50 to 100 copies per minutes. Also, in embodiments the inks of the present invention possess water staining resistance.
Ink jet printing systems can generally be classified as continuous stream and drop-on-demand. In drop-on-demand systems, a droplet is ejected from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not usually formed or expelled unless it is to be placed on the recording medium. A second type of drop-on-demand system is known as thermal ink jet, or bubble jet. With this type, there are apparently generated high velocity droplets and there is allowed very close spacing of the nozzles. Thermal ink jet processes are well known as indicated herein, and are described, for example, in U.S. Pat. Nos. 4,601,777; 4,251,824; 4,410,899; 4,412,224 and 4,532,530, the disclosures of each of which are totally incorporated herein by reference.
Known ink jet inks generally comprise a water soluble dye which is soluble in an ink vehicle such as water or a mixture comprising water and a known water soluble or water miscible organic solvent. Inks comprising these soluble dyes may exhibit many problems, such as poor waterfastness, poor lightfastness, clogging of the jetting channels as a result of solvent evaporation and changes in the solubility of the dye, dye crystallization, ink bleeding when prints are formed on plain papers, poor thermal stability, chemical instability, ease of oxidation, and low drop velocity. In addition, many of these known dyes contained in inks may be potentially toxic or mutagenic. These problems can be minimized by replacing the dyes used in ink formulations with insoluble pigments. Although not being desired to be limited by theory, it is believed in embodiments of the present invention that the improvement in latency can be caused by a complexation between the dye and the grafted dendrimer. Thus, the latency of an ink containing Food Black #2, having the largest number of complexation sites (4 sulfonate groups), is increased much more in presence of the grafted dendrimers than the latency of an ink containing Direct Black 168 (3 sulfonate groups). In general, pigments are superior to dyes with respect to waterfastness, lightfastness, image density, thermal stability, oxidative stability, compatibility with both coated/treated and plain papers, image edge acuity, and nontoxic and nonmutagenic properties.
Heterophase ink jet inks are known. For example, U.S. Pat. No. 4,705,567, the disclosure of which is totally incorporated herein by reference, discloses a heterophase ink jet ink composition which comprises water and a dye covalently attached to a component selected from the group consisting of poly(ethylene glycols) and poly(ethylene imines), which component is complexed with a heteropolyanion. In addition, U.S. Pat. No. 4,597,794 discloses an ink jet recording process which comprises forming droplets of an ink and recording on an image receiving material by using the droplets, wherein the ink is prepared by dispersing fine particles of a pigment into an aqueous dispersion medium containing a polymer having both a hydrophilic and a hydrophobic construction portion. The hydrophilic portion is comprised of a polymer obtained from monomers having mainly polymerizable vinyl groups into which hydrophilic portions such as carboxylic acid groups, sulfonic acid groups, sulfate groups, and the like are introduced. Pigment particle size may be from several microns to several hundred microns. The ink compositions disclosed may also include additives such as surfactants, salts, resins, and dyes.
U.S. Pat. No. 4,877,451, the disclosure of which is totally incorporated herein by reference, discloses ink jet ink compositions comprising water, a solvent, and a plurality of colored particles comprising hydrophilic porous silica particles to the surfaces of which dyes are covalently bonded through silane coupling agents. In addition, in copending application U.S. Ser. No. 07/369,003, the disclosure of which is totally incorporated herein by reference, there are illustrated ink jet inks and liquid developers containing colored particles comprising hydrophilic porous silica particles to the surfaces of which dyes are covalently bonded through silane coupling agents. The ink compositions of this patent are believed to be less stable in the printheads, and less stable during storage, disadvantages avoided, or minimized with the inks of the present invention.
In U.S. Pat. No. 5,120,361, the disclosure of which is totally incorporated herein by reference, there is disclosed an ink composition comprised of a solution comprised of a dendrimer and a dye or dyes, which dyes are visible, or can be seen under normal viewing conditions, and wherein the dendrimer can be a first, second or third generation dendrimer.
In copending application U.S. Ser. No. 904,318, there are illustrated ink jet inks comprised of an aqueous liquid vehicle comprised of certain dyes and dendrimers. In one embodiment, the inks of the copending application are comprised of a solution comprised of a porphyrin type dye and a dendrimer.
In U.S. Pat. No. 5,145,518 there is disclosed an ink composition which comprises an aqueous liquid vehicle and particles of an average diameter of 100 nanometers or less which comprise micelles of block copolymers of the formula ABA, wherein A represents a hydrophilic segment and B represents a hydrophobic segment, and wherein dye molecules are covalently attached to the micelles, said dye molecules being detectable when exposed to radiation outside the visible wavelength range; and in U.S. Ser. No. 834,093 there is disclosed an ink composition comprised of a solution comprised of a dye comprised of a porphyrin chromophore. The disclosures of each of the copending applications are totally incorporated herein by reference.